The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Conventional flash memory stores data by storing electric charges in flash cells. The amount of electric charge stored sets a threshold voltage, which corresponds to a data value. It can be difficult, however, to precisely set an amount of charge to set an exact threshold voltage. As a result, the actual threshold voltages for flash cells in the flash memory often follow a Gaussian distribution centered on a target threshold voltage. The mean of the threshold-voltage distribution is often used as the target threshold voltage when writing to a cell, though this mean is often not the actual threshold voltage for that cell.
Further still, the mean and variance of these threshold-voltage distributions may change. To adapt to such changes, conventional methods estimate the mean and variance of the threshold-voltage distributions using read backs from the flash cells. These conventional methods, however, are often slow to adapt, or are inaccurate in estimating, changes in the threshold-voltage distributions. Without an accurate and timely estimate of the threshold-voltage distributions, writing and reading data from flash memory can be unreliable.